Bread yeast, baker’s yeast, or to give it its scientific name Saccharomyces cerevisiae has been used in baking for thousands of years. Strains of Saccharomyces cerevisiae also ferment rice, barley and wheat sugars for alcoholic drinks. Saccharomyces cerevisiae is also an important and commonly used laboratory model organism. Its power as a research tool comes from the ability to quickly map a phenotype producing gene to a part of the yeast genome.
Yeasts are eukaryotic organisms that are members of the Fungi kingdom. They are unicellular and reproduce asexually by budding, though there are some sexual reproductive life cycles.
Yeast Genome Sequenced
The project to sequence the yeast genome got underway in 1989 and the entire code of strain S288c was spelled out in 1996. Not only was this a major breakthrough of itself, but it also served as a catalyst for the genome sequencing projects that were to follow.
An international consortium of scientists and researchers from 92 laboratories took part in the initiative. They came from the UK, USA, Canada, continental Europe, and Japan.
The yeast genome was found to consist of some 6,000 genes across 16 chromosomes. Four years previously the initiative had announced the full sequence of yeast chromosome III, and it was the first time that a eukaryotic chromosome had been sequenced.
The yeast genome is particularly useful to scientists because it houses many genes that are similar to human genes; about one third of yeast genes are related to those in human. And the yeast genome does not have the large amounts of non-coding DNA that is found in the human genome. It makes finding genes much easier!
Yeast Genome and Research
The yeast genome has been an important model in a whole host of research efforts. Its shorter cell cycle compared to those of higher eukaryotes make it easier to screen compounds and observe cell processes. Much of our understanding of the eukaryotic cell cycle comes from yeast studies, and the microbe’s track record in genetics research is impressive as it has taught us about the ways some genes are inherited together and how genes are turned on and off.
Many of the genes that are involved in the control of the cell cycle are conserved between humans and yeast. Cancer occurs when the cell cycle goes out of control and faulty cells proliferate instead of dying out. It is often the genes that are involved in cell proliferation that are mutated in cancer cells and so yeast can be used to study anticancer drugs to see if they are hitting, and neutralising their molecular targets.
An example of how yeasts have been used in other kinds of medical research comes from the University of Chicago at Illinois. In February 2009 scientists there discovered a prion - an infectious mis-folded protein - inside brewer’s yeast that affects the expression of yeast genes (as does the normal version of the protein). Prions have been associated with degenerative diseases such as “mad cow” and Creutzfeldt-Jakob. It is not known yet whether the actions of prions in yeast are similar to prions in mammals, but the more they are studied the clearer the picture should become.
Basant K. Patel, Jackie Gavin-Smyth, & Susan W. Liebman. The yeast global transcriptional co-repressor protein Cyc8 can propagate as a prion. Nature Cell Biology 11, 344 - 349 (2009) Published online: 15 February 2009 | doi:10.1038/ncb1843